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CBSE Class 12 Maths 2010 Solved Paper

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Question : 16 of 29
Marks: +1, -0
Find the Cartesian equation of the plane passing through the points A (0, 0, 0) and B (3, -1, 2) and parallel to the line x−41\frac{x-4}{1} = y+3−4\frac{y+3}{-4} = z−17\frac{z-1}{7}
Solution:  
Let the equation of plane be ax + by + cz + d = 0 …. (1)
Since the plane passes through the point A (0, 0, 0) and B(3, -1, 2), we have a × 0 + b × 0 + c × 0 + d = 0
⇒ d = 0 …. (2)
Similarly for point B (3, -1 , 2), a x 3 + b x (-1) + c x 2 + d = 0
3a – b + 2c = 0 (Using, d = 0) …(3)
Given equation of the line is
x−41\frac{x-4}{1} = y+3−4\frac{y+3}{-4} = z−17\frac{z-1}{7}
We can also write the above equation as
x−41\frac{x-4}{1} = y−(−3)−4\frac{y-(-3)}{-4} = x−(−1)7\frac{x-(-1)}{7}
The required plane is parallel to the above line.
Therefore, a × 1 + b × (-4) + c × 7= 0
⇒ a – 4b + 7c = 0 … (4)
Cross multiplying equations (3) and (4), we obtain:
a(−1)×7−(−4)×2\frac{a}{(-1)\times 7-(-4)\times 2} = b2×1−3×7\frac{b}{2\times 1-3\times 7} = c3×(−4)−1×(−1)\frac{c}{3\times (-4)-1\times (-1)}
⇒ a−7+8\frac{a}{-7+8} = b2−21\frac{b}{2-21} = c−12+1\frac{c}{-12+1}
⇒ a1\frac{a}{1} = b−19\frac{b}{-19} = c−11\frac{c}{-11} = k
⇒ a = k , b = - 19k , c = - 11k
Substituting the values of a, b and c in equation (1), we obtain the equation of plane as:
kx - 19ky - 11kz + d = 0
⇒ k (x - 19y - 11z) = 0 (From equation(2))
⇒ x - 19y - 11z = 0
So, the equation of the required plane is x – 19y - 11z = 0
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